Sharks have been swimming the world's oceans for millions of years and play a vital role in managing healthy ecosystems. The majority of shark species prey on fish and smaller aquatic life such as mollusks and clams, however, bigger species of sharks generally feed on larger animals such as sea lions, seals and bigger fish.
Sharks have fallen victim to a reputation as fierce man-hunting predators and over the years various cases of shark attacks on humans have been documented.
In order to combat shark attacks, coastlines and beaches are often safeguarded with anti-shark devices to prevent sharks from entering the enclosed swimming areas. Various different anti-shark devices have been used including shark nets, drum lines and exclusion nets.
Shark nets are large-meshed nets designed to entangle and catch sharks, thereby reducing the population thereof within the vicinity of enclosed beaches. These nets are typically secured at two ends by anchors and laid submerged in two parallel rows a few hundred meters offshore and in water depths of approximately 10 to 14 meters. Although fairly effective, shark nets do not form a complete barrier and sharks can swim over, under or around the nets. It is therefore not uncommon for sharks to be found on the shore-side of shark nets and many of these are then often caught in the nets when leaving the protected area. In addition to this, other aquatic creatures such as turtles and dolphins are often caught and killed in the nets.
Drum lines are often used in addition to shark nets and are also designed to attract and capture sharks with baited hooks, rather than to form a barrier between bathers and sharks.
Exclusion nets have smaller mesh sizes and create a physical barrier beyond which sharks, and many other aquatic creatures, cannot pass. They extend vertically from the sea floor to just below the surface. Although exclusion nets are not designed to capture sharks and are therefore generally less detrimental to the environment, the nets are not suitable for certain high-swell regions and are impractical for protecting large areas.